The prior art has described different circuits for obtaining a synthesized sine wave such as for use in frequency shift keying, as in U.S. Pat. No. 3,991,389. Other patents have disclosed means to digitally generate a sine wave, such as U.S. Pat. Nos. 3,659,048 and 3,773,975. Still further, patents of the prior art have suggested a sine or cosine table in the read only memory to be looked up to generate a sine wave, such as in U.S. Pat. Nos. 3,617,941; 3,824,498; 4,259,648; and 4,504,802. Typically, the U.S. Pat. No. 3,793,597 disclosed digital sample points of various modulation levels stored in a ROM and read out in timed sequence to modulate a carrier at a constant depth of modulation. Kim et al. writing in IEEE Transactions on Industry Applications, July 1987, page 654, disclose digital pulse width modulation with sine wave data stored in a ROM. Different modulation levels are disclosed as requiring a very large memory for control of the output voltage.